1. Field of the Invention
The present invention relates to an image displaying apparatus to be mounted on the head for an observer to observe image information displayed on an image display device, and more particularly to an image displaying apparatus arranged to guide a light beam based on the image information displayed on the image display device, such as a liquid crystal image display device, provided in the apparatus, to the observer's eyeball, thereby permitting the observer to observe the image information as an enlarged, virtual image.
2. Related Background Art
A large-area monitor apparatus is necessary for forming a large-screen image with presence in conventional television displaying apparatus. Such large-screen monitors had such problems that they were expensive, that the apparatus per se became large in scale, and that a wide space was necessary for appreciation.
Methods for decreasing the size of these displaying apparatus have been proposed to solve such problems, for example in Japanese Laid-open Patent Applications No. 62-127826 and No. 1-133479. In these applications, there are proposed the apparatus arranged to enlarge an image on a small-area image display device and to display an enlarged, virtual image equivalent to a large-screen image so as to permit the observer to observe it. Also, National Publication of Translated Version of Japanese Patent Application No. 4-501637 describes a proposal of stereo video image display apparatus arranged in such a manner that two stereoscopically recorded images are displayed on respective image display devices corresponding to the left and right eyes, that enlarged, virtual images of those displayed images through optical systems are superimposed ahead the observer by a small mirror in front of the observer's pupils, and that the external field can be visually recognized around the displayed, virtual images.
Besides, Japanese Laid-open Patent Applications No. 6-38144 and No. 6-43392 also proposed the miniaturized, displaying apparatus.
The apparatus of this type have an advantage that the observer can observe an image while moving or doing another work, in addition to an advantage that the apparatus can show a large-screen image as being compact.
For the displaying apparatus arranged for double observation of a scene in the external field and the enlarged, virtual image of image information displayed on the image display device (hereinafter referred to as a virtual display image), there are two ways for observing the images. One of them is a case for observing or visually recognizing only either one of the scene in the external field and the virtual display image as selectively selected. In this case, the virtual display image is largely displayed in the field which the observer is visually recognizing, and visual recognition may be made while changing over the observing field between the scene in the external field and the virtual display image by an on-off changeover switch and means for shutting off the scene in the external field.
The second case is a case of superimposed observation in which the virtual display image is superimposed on the scene. For example, the second case includes a case in which a variety of meters and symbols for pilotage are superimposed in a pilot field of airplane, a case for evaluating an effect of an object to be set in a scene by superimposing a building or sculpture in a scene on the ground, or a case for appreciating a video image in a size not to cause a trouble in observation of scene, while mainly observing the scene in the external field.
For the displaying apparatus for superimposed observation of the virtual display image superimposed on the scene in the external field, when the size of virtual display image is desired to change or when the position of virtual display image is also desired to change, it is conceivable that the region utilized for display on a display surface of the image display device is demagnified with necessity, thereby decreasing the size of the virtual display image. In this case, a decrease in the number of pixels is extreme in the image display device operating for display of image information, resulting in unsatisfactory image quality.
In case of the apparatus as proposed in Japanese Laid-open Patent Applications No. 6-38144 and No. 6-43392, a moving amount of moving portions becomes very large in order to attain a large magnification change, which is not preferred for the display apparatus to be mounted on the head.